This application claims the priority of German Patent Document 100 06 513.9, filed in Germany, Feb. 15, 2000, the disclosures of which is expressly incorporated by reference herein.
The invention relates to an air conditioning system for a motor vehicle.
Preferred embodiments relate to such an air conditioning system which is designed for an air conditioning operating mode and at least one other operating mode in the form of at least one of a heat pump operating mode and a reheat operating mode, said air conditioning system comprising:                a refrigerant cycle with a compressor, a refrigerant cooler and a supply air/refrigerant heat exchanger, said supply air/refrigerant heat exchanger being disposed in a supply air channel and functioning as an evaporator in an air conditioning operating mode,        a coolant cycle for cooling a heat generating vehicle component,        a refrigerant/coolant heat exchanger, coupling the refrigerant cycle and the coolant cycle so as to transfer heat, and        refrigerant flow control valves for controlling mode-dependent dependent flow of the refrigerant so as to be guided in an air conditioning mode from the compressor over the refrigerant cooler to the supply air/refrigerant heat exchanger.        
Air conditioning systems of the type referred to can be operated selectively, i.e. reversibly, in an air conditioning operating mode and at least one other operating mode, in particular a heat pump operating mode and/or a reheat operating mode, and are designed correspondingly to this end. This feature comprises in particular the presence of a refrigerant cycle, on the one hand, and a coolant cycle, on the other hand, both of which transfer heat and are coupled by a refrigerant/coolant heat exchanger. In the air conditioning mode the supply air/refrigerant heat exchanger works as an evaporator, which cools the supply air, in order to pass it then, for example, into the vehicle interior. In the heat pump mode the supply air/refrigerant heat exchanger functions as a heater by reversing the refrigerant's direction of flow in order to heat the supply air. In this case the refrigerant/coolant heat exchanger functions as an evaporator, which extracts the heat from the coolant and uses said heat to evaporate the refrigerant. In the reheat mode the supply air is cooled in the supply air/refrigerant heat exchanger, functioning as an evaporator, and heated again in a supply air/coolant heat exchanger, functioning as a heater. Suitable refrigerants are, for example, carbon dioxide and R134a. The coolant cycle serves to cool a heat generating vehicle component, which can be in particular an internal combustion engine, functioning as the vehicle drive motor, where a mixture of water and glycol are usually used as the coolant.
An air conditioning system of the aforementioned type is described in the published patent application (Offenlegungsschrift) DE 198 06 654 A1. In said arrangement the coolant can be fed, after passing the housing of an internal combustion engine, in a controlled manner to the refrigerant/coolant heat exchanger and/or to a supply air/coolant heat exchanger, which runs parallel in the coolant cycle, and/or a coolant cooler, which is also arranged parallel in the coolant cycle. The latter is usually defined as a cooling air/coolant heat exchanger, which cools the coolant with ambient air. The refrigerant cycle of this prior art air conditioning system comprises, among other things, a medium pressure accumulator, to which an expansion element is attached on both sides. Both of them must be designed in such a manner that the throughflow is bidirectional.
In addition, there exist various other types of this class of air conditioning system that can be operated selectively at least in the air conditioning mode or in the heat pump mode and/or reheat mode. Thus, an air conditioning system, described in the publication by A. Hafner et al., “An Automobile HVAC System with CO2 as the Refrigerant”, IIF-IIR—Sections B and E, Oslo, Norway, 1998, page 289, exhibits two supply air/refrigerant heat exchangers, both of which function as evaporators in the air conditioning mode, whereas in a heating or heat pump mode, designed as a reheating operation, the supply air/refrigerant heat exchanger, which is downstream in the supply air's direction of flow, functions as a heater for heating the supply air. To control the flow of refrigerant, a 4 way valve and a 3 way valve are provided. In addition, the refrigerant cycle comprises an internal heat exchanger, a low pressure-sided accumulator and an exhaust air/refrigerant heat exchanger for heat recovery. In the heat pump mode, a refrigerant/coolant heat exchanger, which couples the CO2 operated refrigerant cycle with a coolant cycle of the internal combustion engine of a vehicle drive, transfers heat from the coolant to the refrigerant, whereas it functions inversely in the cooling mode as a refrigerant cooler, which transfers the heat from the refrigerant to the coolant. To this end, it is coupled in the air conditioning mode on the input side of the refrigerant to the output side of a compressor of the refrigerant cycle.
The textbook contribution by Y. Noda et al., chapter 5.1 “Development of Twin-Heated Ventilation and Air Conditioning System (ThVACS)” in Heat Management of Vehicles, edited by N. Deuessen (ed.), expert-verlag, page 227, describes an air conditioning system, in which a heat exchanger, working as a condenser in the air conditioning mode, is bypassed by the high pressure-sided refrigerant stream in a heating mode, designed as a reheat mode. Instead, said high pressure-sided refrigerant stream is fed to an auxiliary condenser, disposed in a supply air channel, and from there fed to an evaporator, connected upstream in series to an auxiliary condenser in the supply air channel. The refrigerant, issuing from the evaporator, is guided over a refrigerant/coolant heat exchanger, designed as an auxiliary evaporator, and from there over an accumulator to a compressor. In the coolant cycle, with which the vehicle drive internal combustion engine is cooled, there is, among other things, a heater, disposed in the supply air channel.
In an air conditioning system, disclosed in the U.S. Pat. No. 5,641,016, with selective air conditioning and heat pump mode, a refrigerant cycle and a coolant cycle are coupled by means of a refrigerant/coolant heat exchanger, which is disposed, independently of the operating mode, on the refrigerant side between the compressor and a refrigerant cooler. In heat pump mode, an evaporator, arranged in the supply air channel, is bypassed by the refrigerant stream. The coolant cycle, which uses water as the coolant, absorbs exhaust heat from, among other things, a vehicle drive internal combustion engine and can also be heated, as desired, by a burner. The supply air can be heated by heated cooling water by means of a supply air/coolant heat exchanger, arranged in the supply air channel.
The use of air conditioning systems of the aforementioned type is especially important for low consumption vehicles, which exhibit an internal combustion engine, e.g. a diesel engine, as the drive motor. Said diesel engine exhibits direct injection and a relatively low fuel consumption and, therefore, generates, comparatively little exhaust heat, which by itself is no longer adequate to heat the interior of the vehicle to a comfortable temperature level in an acceptable period of time with the coolant cycle. Not even defrosting the front windshield and side windows is guaranteed in each case with just the exhaust heat of such a low consumption engine. Of course, a number of additional heating designs have been proposed to cover this heat capacity deficit. They use the primary energy from fuel either directly by burning the fuel in a burner or by converting into heat a portion of the mechanical shaft output of the internal combustion engine by means of a suitable energy converter and feed the heat to the interior either directly, e.g. by means of PTC [=positive temperature coefficient] heating elements, or by means of the coolant, e.g. by means of viscous heaters or retarders. However, these solutions require an additional consumption of fuel at a usually unsatisfactory ratio of additional heating capacity to primary energy consumption and/or are so unproductive that the spontaneous heating capacity is not significantly improved and, therefore, the heating dynamics cannot be significantly improved at least in the first part of the heating phase. Another attempt to solve this problem endeavors to reduce the heat requirement through an increase in air circulation in combination with circulating air driers or heat recovery from the outgoing air of the interior. In this manner it is at least possible to lower the heating capacity requirement during the stationary heating mode, but the time required to heat up an initially cold vehicle interior cannot be significantly shortened.
The invention is also based on the technical problem of providing an air conditioning system of the aforementioned class that with relatively simple means permits the option of not only an air conditioning mode but also an effective heat pump and/or reheat mode. Moreover, the invention avoids the known problem of re-evaporation of the water of condensation from the supply air/refrigerant heat exchanger, which is used as the evaporator as a function of the operating mode, into the supply air, passed into the interior of the vehicle.
Preferred embodiments of the invention solve these problems by providing an air conditioning system for a motor vehicle, which is designed for an air conditioning operating mode and at least one other operating mode in the form of at least one of a heat pump operating mode and a reheat operating mode, said air conditioning system comprising:
a refrigerant cycle with a compressor, a refrigerant cooler and a supply air/refrigerant heat exchanger, said supply air/refrigerant heat exchanger being disposed in a supply air channel of an air supply conveying unit and functioning as an evaporator in an air conditioning operating mode,
characterized by one or more of the following features:                (a) the provision of an internal combustion engine exhaust gas/coolant heat exchanger connected upstream in series to the refrigerant/coolant heat exchanger in the coolant cycle        (b) the provision that said at least one other operating mode includes a reheat operating mode, in which the refrigerant flow control valves guide refrigerant flow from the compressor at least in part to the refrigerant/coolant heat exchanger, functioning as the condenser/gas cooler in this operating mode, and from there to the supply air/refrigerant heat exchanger, functioning as the evaporator in this operating mode, and        wherein the refrigerant/coolant heat exchanger is connected upstream in series on the coolant side to a supply air/coolant heat exchanger disposed in the supply air channel; and        (c) the provision that the supply air conveying unit exhibits two operating modes with opposite supply air conveying directions, and        wherein the air conditioning system is designed for carrying out a drying operating mode, in that the supply air conveying unit conveys drying air for drying the supply air/refrigerant heat exchanger in the air conveying direction, reversed to the supply air conveying direction leading into the vehicle interior, past the supply air/refrigerant heat exchanger, whereby the drying mode is activated at least after shutdown of the vehicle in a previous air conditioning or reheat mode.        
In the air conditioning system, according to certain is preferred embodiments of the invention, an internal combustion engine exhaust gas/coolant heat exchanger is connected upstream in series with the refrigerant/coolant heat exchanger in the coolant cycle. This feature enables the use not only of the exhaust heat, generated in the internal combustion engine itself but also the heat of the exhaust gas, emitted by said engine, e.g. in a heat pump operating mode of the air conditioning system. In this manner the goal of heating the supply air comparatively fast for the purpose of quickly heating up the initially cold vehicle interior is attained, since in the case of a cold start the exhaust gas from the engine is the medium with the fastest temperature increase.
The air conditioning system, according to certain preferred embodiments of the invention, is designed to carry out a specific reheat operating mode, wherein the refrigerant/coolant heat exchanger functions as the condenser/gas cooler of the refrigerant cycle and is connected upstream in series to a supply air/coolant heat exchanger, functioning as the heater, in the coolant cycle. Said supply air/coolant heat exchanger is disposed in turn in a supply air flow channel behind the supply air/refrigerant heat exchanger, functioning as the evaporator. Thus, the heat, withdrawn from the supply air at the evaporator in the refrigerant cycle, can be fed again for the purpose of heating by means of the refrigerant/coolant heat exchanger and the supply air/coolant heat exchanger to the supply air stream, which has been cooled for the purpose of drying. In addition, the engine exhaust heat can be used, if present, for heating the supply air.
It is preferred in conjunction with certain embodiments of the invention that, in the coolant cycle, the internal combustion engine exhaust gas/coolant heat exchanger is connected upstream in series to the refrigerant/coolant heat exchanger so that the exhaust gas heat can also be used to reheat the supply air, a feature that is especially expedient in the case of a cold start at low external temperatures and the use of a low consumption engine in order to achieve effective reheating.
In a further development of preferred embodiments of the invention, the refrigerant flow controller, which suitably controls the refrigerant flow in the different operating modes, includes a 4 way valve and a 3 way valve. The refrigerant/coolant heat exchanger, the refrigerant cooler and the 4 way valve are attached to the 3 way valve, whereas the supply air/refrigerant heat exchanger and the inlet and the outlet side of the compressor are connected not only to the 3 way valve but also directly or indirectly to the 4 way valve. With this valve configuration the direction of the refrigerant flow can be reversed. In addition, the refrigerant/coolant heat exchanger or the refrigerant cooler or both can be switched selectively into the active refrigerant cycle.
According to another advantageous feature of certain preferred embodiments of the invention, the high pressure-sided accumulator in the refrigerant cycle includes a check valve arrangement, which suitably connects the accumulator on the inlet and outlet side to the refrigerant cooler, the supply air/refrigerant heat exchanger, and the refrigerant/coolant heat exchanger. As an alternative advantageous feature of certain preferred embodiments of the invention, a low pressure-sided accumulator is provided in combination with an internal heat exchanger.
Certain preferred embodiments of an air conditioning system, according to the invention include a supply air conveying unit, which can be switched over into a first or a reversed, second conveying direction, and with which the air conditioning system can be operated in a drying operating mode by means of corresponding controlling means. In this mode the flow direction of the supply air is reversed by way of the supply air/refrigerant heat exchanger into that in the one or the other operating mode. Thus, the supply air/refrigerant heat exchanger can be dried when in the previous operating mode water of condensation has condensed on said heat exchanger so that no moist air passes into the vehicle interior. This is especially useful for restarting the vehicle in cases where the air conditioning system was in air conditioning or reheating mode when the vehicle was previously turned off.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.